Wednesday, December 30, 2009

As with megavitamin "therapy", hyperbaric oxygen as a "treatment" for autism can be accurately classed as too much of a good thing.

In medicine, too much of a good thing can be a very bad thing, and the research reflects this. Essential nutrients can easily become poisons if you consume too much of them, and many of today's common medical problems can be laid at the feet of too much consumption of essential macronutrients... and macronutrients are generally far better tolerated than the micronutrients which are used to excess in "megavitamin therapy".

In fact, hyperbaric oxygen chambers allow for a greater exposure to oxygen than would normally be theoretically possible. Put into more technical language, a hyperbaric chamber allows for partial pressures of oxygen within the lung that wouldn't be possible without active pressurization.

While this isn't the only mechanism of action for HBOT (for instance, the increased overall pressure has therapeutic value when treating decompression sickness), it's the main one, and the one which most of the various explanations of HBOT as an autism treatment hinge upon. Specifically, increased partial pressure is increased effective in-lung exposure to oxygen, and this is supposed to increase oxygen content in the bloodstream, increase oxygen flow to the brain, etc., etc.

Oxygen qualifies as a drug when used this way. As with vitamins, it's quite possible to overdose on it. This is known by a variety of names, but the most common of these are "oxygen toxicity" (for the phenomenon) and "oxygen poisoning" (for the medical condition).

Frankly, oxygen poisoning can be nasty. At lower levels, oxygen is a very good thing. At higher levels... it isn't. In fact, oxygen has neurotoxic properties at high enough doses, and these doses are acheivable even without a hyperbaric chamber.

So, if that's the case, why is it that that we don't see autistic children vomitting, suffering from tunnel vision and shortness of breath, convulsing, twitching, and generally showing the symptoms of oxygen poisoning after HBOT? The answer is actually rather simple -- and says a lot about the people peddling HBOT for autism.

The partial pressure of a gas within a mixture is equal to the percentage of the mix formed of that gas times the total pressure of the gas. So, for instance, the partial pressure of oxygen in a gas mixture which contains 20% oxygen and is held at 1 bar (normal atmospheric pressure) is .2 bar. Doubling either the percentage of gas or the overall pressure of the mix will also double the partial pressure of oxygen, yielding a partial pressure of .4 bar.

It's worth noting that a partial pressure of up to about one bar (depending on altitude, weather patterns, and just about anything else that effects atmospheric pressure) is achievable without pressurization -- 1 bar is the partial pressure of oxygen in a pure oxygen "mix" at normal atmospheric pressure. Keep that in mind as I continue.

A recent paper, using fairly typical practice for HBOT treatment for autism, used a 24% oxygen mix at 1.3 bar of pressure. Doing the math, this yields a partial pressure of about .31 bar... or roughly equivalent to what could be acheived by using a 31% oxygen mix without the hyperbaric chamber. It's actually pretty trivial to go to a SCUBA supply shop and buy a tank full of a mix that's richer in oxygen than that.

Of course, typical air is roughly 21% oxygen, meaning that the gas they used was only trivially different from room air in terms of oxygen content; the increase in partial pressure was almost entirely achieved by a raise in pressure.

While this sort of level is typical in practice, however, it's worth noting that I've seen documentation of much more "intense" regimens, ranging up to 100% oxygen at 1.5 bar. Caveat emptor -- and beware oxygen poisoning.

Finally, I suppose I should also mention that there's a second theorized action mechanism, involving gas transport via blood plasma (as opposed to the hemogloboin-based transport of red blood cells), which is increased substantially under hyperbaric conditions. This mechanism is equally implausible for reasons which are much harder to explain, but I should probably mention it in the interest of fairness.

Still -- 1.3 bar isn't enough pressure to make much of a difference there, either.

Friday, December 11, 2009

Fellow bloggers Kim Wombles, Thelma, and Louise have started an effort to form a new autism organization, one which actually looks pretty good... if still young. I hold out great hopes for their efforts.

Edit: I somehow managed to miss Kathleen's involvement with the project. She deserves a mention as well. Again -- good luck!

At the same time, the anti-disease group PKIDs has released a pretty spectacular set of videos on the horrific costs that the decision not to vaccinate can impose on families. Sullivan of LBRB has blogged on them here, complete with embedded video.

In his post, however, Sullivan wrote the following:

For any who wish to comment that this has nothing to do with autism, I agree. Unfortunately, the autism community is one of the biggest sources of misinformation about vaccines and vaccine preventable diseases. If I can help PKIDs a bit with this post, I see that as a good thing.

I have to somewhat disagree. Ideally, he is right -- this shouldn't have anything to do with autism. His comment that the autism community is one of the biggest sources of misinformation about vaccines and vaccine preventable illnesses, however, hits the nail on the head.

The instant vaccines entered the autism discussion, the two became connected. Despite the fact that the connection is purely artificial, a product of quackery and delusion, it is very real... and very horrifying.

Watch those videos. I'm particularly fond of the Hib, Hepatitis, and pneumococcal disease videos, but the others are generally pretty good as well.

This is what groups like DAN and Generation Rescue are telling people to risk rather than accept a percieved risk of having their kids turn out like us. This is what they are telling people is better than autism when they advise parents not to vaccinate their children.

Thursday, December 10, 2009

Bad information is far more common than good on the Internet, especially in complex and often ambiguous fields such as medicine. This should not be a surprise to anyone -- while it takes a great deal of effort to assemble good information, bad information is far easier to put together.

As such, finding the good information -- via free services, anyway -- is often a matter of combing for a metaphorical needle in a haystack, and the information you find is often highly skewed in a variety of ways even when it is of decent quality.

I regularly read blogs maintained by doctors and researchers, for instance. While they provide news and often-educational commentary, their commentary on basic issues is usually provided on an ad hoc and incomplete manner as parts of explanations on other matters. This is fine if you already understand the basic issues involved, but if you're trying to educate yourself on issues surrounding the use of the P value in hypothesis testing, for instance, comments on what Study X did wrong will only take you so far.

This is particularly vexing when running a blog and attempting to provide references for the concepts in question. I try to write my articles in such a way that a naive reader can educate himself on the relevant issues with a minimum of fuss; as such, I often need a bit more than I can easily find in other blogs.

Because of this, it was an extremely pleasant surprise for me to find out that one of my favorite basic introductions to P values and the general nature of statistical hypothesis testing is available for free. I'd originally gotten access to it through my university, so I didn't realize at first, but this really has renewed my awareness of the free articles available on the Internet -- and the value of the available literature on how to interpret the literature.

In other words -- I'm happy about this, even if I'm far less so about the way my left knee's acting up. Joint instability is not fun.